1. Field of the Invention
The present invention relates to an illuminating device for use in a photographic apparatus of a fundus oculi.
2. Description of the Prior Art
An ophthalmoscopic photographic apparatus is used to inspect retinal hemorrhage, ablatio retinae, arteriosclerosis or the like. In the conventional photographic apparatus of fundus oculi the optical system thereof is as shown in FIG. 1, in which reference numeral 1 is a light source for observation, 2 is a condenser lens for observation, 3 is a light source for photographing, 4 is a condenser lens for photographing, 5 is a half-mirror, 6 is a ring slit, 7, 8 and 9 are lenses for illuminating, 10 is a reflecting mirror, 11 is a reflecting mirror with an aperture, 12 is an objective lens, 13 is an eye to be inspected, 14 is a photographic lens, 15 is a reflecting mirror for switching optical path, 16 is a reflecting prism, 17 is an ocular, and 18 is a film surface. In such a conventionally used photographic apparatus of fundus oculi, when observation is carried out with the use of a light source for observation, illumination light from the light source 1 for observation is reflected by the half-mirror 5 through the condenser lens 2 for observation so as to change its light path, and projected on the ring slit 6. Further, the illumination light passed through the ring slit 6 and the lens 7 is again changed its light path by the reflecting mirror 10, and then projected on the reflecting mirror 11 with the aperture by means of each lens 8, 9. Furthermore, the illuminating light reflected by the reflecting mirror 11 with the aperture is projected on the cornea of the eye 13 to be inspected by means of the objective lens 12 and then the light illuminates the retina of the eye to be inspected. Then, the light reflected by the retina passes again through the objective lens 12 and the light transmitted through the aperture of the reflecting mirror 11 is observed as an image of the retina by means of the ocular 17 through the lens 14, the reflecting mirror 15 and the reflecting prism 16.
On the other hand, in case of photographing, the illumination light for photographing emitted from the light source 3 passes through the half-mirror 5 by means of the condenser lens 4, and projected on the ring slit 6, so that the light illuminates the retina of the eye 13 to be inspected as explained in the case of the aforementioned observation. Further, the light reflected on the retina is also directed to the direction of the lens 14. In this case, the reflecting mirror 15 is switched to the position shown by a dotted line, so that the light reflected on the retina is focussed and imaged on the film surface 18 by means of the lens 14 and photographed.
In the conventional photographic apparatus of the fundus oculi explained in the above, both the illumination light from the light source 1 for observation and the illumination light from the light source 3 for photographing are projected on the ring slit 6 by means of the condenser lens 2 or the condenser lens 4, respectively, and then the light transmitted through the portion 6a of the ring slit 6 shown in FIG. 2 is utilized for illumination, but the light through other portion, for example the central portion 6b, is interrupted. However, strength of the light from the light source projected by the condenser lens is brightest at the center and darker around the periphery. Therefore, in the illuminating method for the conventional photographic apparatus of the fundus oculi, the brightest portion of the illumination light from the light source is cut off, so that such method is not efficient in the point of light strength. Further, this method uses the lenses 7, 8, 9 and the reflecting mirror 10 as an illumination optical system, so that a loss of a light amount due to reflection on the lens surface is present and not preferable.
Further, the ring slit 6 and the reflecting mirror 11 with the aperture are same in size, so that an image produced by the illumination optical systems 7, 8 and 9 of the ring slit 6 must be projected precisely on the reflecting surface of the reflecting mirror 11. Accordingly, there is such a problem that the ring slit 6, the reflecting mirror 11 with the aperture, the reflecting mirror 10, and the illuminating optical systems 7, 8, 9 must precisely be centered with each other.